1. Field of the Invention
The present invention relates to optical assemblies and systems and methods for optical packaging of optical components including diode lasers, optical fibers and optical detectors. More particularly, the present invention relates to optical networking units and optical packaging of optical components used in optical networking units.
2. Background of the Prior Art and Related Information
In various applications is necessary to package optical components, such as diode lasers, optical detectors, beam splitters and optical fibers, in compact optical packages while at the same time controlling the precise relationship of the optical elements. For example, one such application of significant commercial importance involves the optical systems employed in fiber optic data distribution networks. Such fiber optic data distribution networks are becoming increasingly important for the provision of high bandwidth data to commercial and residential locations as well as providing conventional voice and/or cable TV (CATV) signals. Such systems employ optical networking units of various types throughout the fiber optic distribution network.
For example, one type of optical networking unit may comprise a diode laser and an optical fiber configured in a package to allow data transmission from the laser into the optical fiber. To minimize losses of the laser light entering the fiber a precise relationship between the laser and the optical fiber must be provided and maintained. Another type of optical networking unit employed in the fiber optic distribution networks may employ an optical fiber aligned with an optical detector in a compact package. In this type of optical assembly it is also very important to ensure a precise relationship between the optical fiber and the detector to have accurate detection of the modulated light provided from the fiber. Other types of optical assemblies used in fiber optic distribution networks include combinations of diode lasers and detectors optically coupled to a fiber. Typically such combinations of detectors and lasers also require a beam splitter. Such beam splitter must also be properly aligned relative to the light beam path between the other optical elements. Other optical components may also be provided, for example, lenses and filters may also be combined in a single optical package comprising an optical networking unit.
Typically, the active optical components in an optical networking unit, such as the diode laser and photodetector are configured in standardized packages, such as transistor outline packages (TO can) which are generally cylindrical packages having leads extending from one side thereof. The optical fiber is typically provided in a ferrule which may be of standardized size and configuration for various network systems. The various passive components, i.e. lenses, filters and beam splitters, in turn may be provided in various configurations and/or packages. In all these cases, and with all these configurations of components, it is critically important that precise alignment is provided and maintained between the different optical elements in the optical assembly.
In addition to having precisely aligned components, optical networking units must be compact and relatively inexpensive to assemble. Since large numbers of such optical networking units are employed throughout a fiber optic distribution system, and since at various nodes or other points in the distribution system relatively large numbers of individual optical networking units may be combined at a single location, the combination of size and cost of the individual units may be very important to the effectiveness of the overall system. Clearly, however, as the optical package size is reduced it becomes more difficult to precisely align the optical elements and keep the cost of the unit low at the same time. Also, as fiber optics based data distribution approaches the consumer the requirement to reduce cost while maintaining precise tolerances in the optical elements included in the optical networking units pose the stringiest demands on the optical package construction and assembly.
In current approaches to packaging of optical components in optical networking units, a metal housing is provided with cylindrical holes used to receive the TO cans holding the various active optical components. A tightly aligned cylindrical hole is also typically provided for the optical fiber ferrule. The holes provided in the metal housing are typically given relatively loose tolerances to allow the optical components to be adjusted for more precise alignment during assembly. Once the components are more accurately aligned the components are fixed in place using various techniques such as laser welding, screw set plus epoxy, or epoxy only. This two-step process of first providing tolerance holes in a housing and then aligning and fixing the optical components is necessary since the parts vary slightly from one to another and the inaccuracies accumulated between the parts requires active alignment of the optical element in relationship with the fiber and also sufficiently accurate positioning of the holes in the housing is impractical for conventional machining or other metal processing in a cost effective manner. Also, even if the holes in the housing can be sufficiently accurately provided, nonetheless there is significant variation between batches of optical components and even individual optical components from a single batch. Therefore, a fixed alignment configuration in the housing cannot accommodate individual variations in the optical components. This two-step process is itself limited in accuracy, however, since it is difficult to maintain the orientation and alignment of the components during the fixing process. Also, this two-step approach introduces additional costs to the assembly process since it is poorly adapted to any type of automation.
Although this problem of providing a compact accurately aligned assembly of optical elements is particularly significant in the area of optical networking units due to the high degree of stability and precision placed on such units due to the placement accuracy requirements of modern single mode fiber optic data distribution systems, it will be appreciated that similar problems exist in a variety of other applications involving optical packaging of optical components.
Accordingly, it will be appreciated that a need presently exists for optical assemblies and systems and methods for optical packaging of optical elements including diode lasers, optical fibers, optical detectors, beam splitters, lens and filters, in a manner which provides a compact yet precisely aligned configuration. Furthermore, a need presently exists for such a system and method which can provide such a compact accurate configuration of optical components in a cost effective manner and which may be adapted for relatively high-volume production.
The present invention provides an optical networking unit employing an optimal packaging of optical components which provides both a compact configuration and a high degree of accuracy in the alignment of the various optical components. The present invention further provides a method for packaging optical components into such an optimized assembly in a manner which reduces the manufacturing costs and which is suitable for relatively high-volume production.
In a first aspect, a preferred embodiment of the present invention provides an optical networking unit comprising a substrate composed of a material transparent to radiation in a frequency range. An optical fiber holder is secured to the substrate and an optical fiber is secured to the optical fiber holder. An active optical component holder is also secured to the substrate and an active optical component, optically aligned with said optical fiber, is secured to the active optical component holder. At least one of the optical fiber holder and active optical component holder is secured to the substrate by a curable bonding material of a type curable in response to exposure to radiation in the frequency range. For example, the bonding material may be a UV curable adhesive and the substrate composed of a material transparent to UV radiation. In one preferred embodiment, the active optical component comprises a diode laser. In another preferred embodiment, the active optical component comprises a photodetector.
In a further aspect of the present invention, additional active optical components may be provided in the optical networking unit. For example, a photodetector may be provided as a second active optical component to detect modulated light provided from the optical fiber. Such detection may be provided along with the transmission of modulated light to the fiber if the first active optical component is a laser. Alternatively, detection of two different wavelengths of modulated light may be provided by the optical networking unit if the first active optical component is also a photodetector. Alternatively, emission of two different wavelengths of modulated light may be provided by the optical networking unit if the first and second active optical component are lasers of different wavelength. The additional active optical component may also be secured to a holder which is bonded to the substrate by a radiation curable adhesive. Passive optical components may also be provided, such as beam splitters, lenses, optical isolators, prisms, and filters. These may be secured to the optical fiber holder, active optical component holder, or directly to the substrate.
A third active optical component may also be provided in another aspect of the invention, which component may also be a photodetector in a preferred embodiment. This aspect of the invention may provide detection of two wavelengths of light from the optical fiber and transmission of a third wavelength to the fiber by the laser. Alternatively, detection of three different wavelengths may be provided.
In a further aspect the present invention provides a method of assembling optical components into an optical assembly. In a preferred embodiment the method comprises providing a first optical component and a second optical component and aligning the first and second optical components in a desired optical configuration. A transparent substrate is also provided. The first and second optical components are secured to the substrate in their aligned configuration by exposing a radiation curable bonding material through the substrate while maintaining the relative configuration of the optical components. For example, UV light and a UV curable adhesive may be employed.
Preferably the act of aligning comprises monitoring the output of at least one of the optical components while adjusting the relative configuration of the components to optimize the optical coupling of the components. The method may further comprise mounting the first optical component to a first optical component holder and the second optical component to a second optical component holder.
The act of securing may then comprise securing the optical component holders to the substrate.
In yet a further aspect the present invention provides an optical assembly comprising plural optical components secured to a substrate, wherein at least one of the components is secured to the substrate with a radiation curable bonding material.
Further features and advantages of the present invention will be appreciated by review of the following detailed description of the present invention.